1. Field of the Invention
This invention relates generally to actuators and, more particularly, to a transmission improvement for an actuator.
2. Related Art
Many mechanical devices need to be moved to a user selected position and then held there against a force that is biased to return the device to its original position. Such devices are commonly used for ergonomic supports in seating, especially lumbar supports for automobile seats. Lumbar supports exert a comfortable force against the lumbar spine of a seat occupant. This force is applied mechanically through a wide variety of configurations including arching, bending, tightening, extending or otherwise moving a pressure surface. Pressure surfaces are of an equally wide variety including straps, paddles, “baskets,” arching surfaces, bowed surfaces and so forth. These devices must allow the user to select a desired position for the pressure surface, and thereafter hold that position after the user has released whatever device and linkage has been used to move the pressure surface to the selected position. The linkages are of a wide variety including rods, levers, springs, cables, and especially coaxial traction cables such as Bowden cables. The linkage, for example a Bowden cable, has a connection to the lumbar support at one end and a connection to an actuator at the other end. The actuator is positioned where the user may operate it, typically at the edge of the seat.
There is a great variety of actuator structures used for these purposes, both mechanical and electrical. They share in common the function of moving the pressure surface to a selected position, and then holding the pressure surface in that position against a force exerted by the seat occupant's weight. That force is biased towards returning the pressure surface to its original position, which is usually flat. The most common linkage, the Bowden cable, has a flexible conduit, also called a “sleeve” or “sheath,” through which runs a coaxially sliding wire. Actuators have a seat for the end of the sleeve and seat for the end of the wire. The opposite ends of the wire and sleeve are connected to different portions of the lumbar or other ergonomic support, such that pulling the wire through the sleeve moves the pressure surface to the desired position. Accordingly, the most commonly used actuators are designed to pull a Bowden cable wire through a Bowden cable sleeve. The actuators must exert the force necessary to pull the wire through the sleeve to actuate the lumbar support. They must also hold the wire against the return force of the passenger's weight on the lumbar support pulling the wire back into the sleeve. In addition the actuators must also be able to release the holding force from the wire so that the user may return the ergonomic device to its original position or to another selected position.
Actuators achieve these necessary functions of movement, holding and release through a variety of mechanisms. Electronically powered actuators frequently use gears connected to take up wheels or drums for pulling the Bowden cable wire. Manual actuators may also use gears and take up drums, but more typically include a brake, ratchet or clutch. Brakes, ratchets and clutches are powered by levers or hand wheels turned by the users hand.
Previously, a single worm/worm wheel transmission was used to operate the Bowden cable. This design fails to eliminate axial loads on the actuator motor shaft. Consequently, it causes the shaft to move axially in its housing and hit the end of it repeatedly, producing an undesirable clicking noice. There is a need to control unwanted axial motion of the motor shaft worm assembly. There is a continuing need to control radial and transverse motion of the shaft worm assembly.
The single worm/worm wheel meshing design also has a lower efficiency for power transmission and requires a higher reduction rate if the other conditions are the same. There is a need for greater efficiency.
Typically, the worm and worm wheel module is undersized to save space, and the insufficient mechanical strength of the single worm/worm wheel transmission often results in tooth breakage. The axial motion causes rapid wear of the washer at the end of the shafts. There is a need for greater durability.
There remains a continuing need in the art for reducing the size and the profile of the assembled actuator. There also remains a continuing need in the art for easing and streamlining assembly of the component parts of the actuator. Finally, there is a continuing need to reduce the number, and consequently the expense, of the components to be assembled into actuators.